Co-combustion Characteristics And Engineering Application Of Biomass And Coal

With the critical energy shortage and global environment concern in the world, biomass with carbon element is regarded as one of the potential renewable energy resources to substitute conventional fossil fuels, such as coal, petroleum and natural gas. Among various thermo-chemical conversion technologies, the co-combustion of biomass and coal in the circulating fluidized bed is now regarded as a simple and efficient method to convert into heat and electricity.The utilization routes of biomass are outlined and the methods for co-firing biomass and coal are introduced with a highlight on circulating fluidized bed combustion in this thesis. Independent combustion and co-combustion profiles of two kinds of coal(lignite and high-sulphur bituminous coal) with two kinds of biomass (energy plant and tobacco stem) are investigated by using thermogravimetric analysis method. Ignition and burnout performances, heat release performances, and gaseous pollutant emissions are also explored in this thesis. The results indicate that weight loss of bioamss combustion is more higher than that of coal combustion, mainly shown biomass as a fast chemical reaction in short time but coal as a slow reaction during the whole combution process. Taking ignition and burnout characteristics, heat release performances, and gaseous pollutant emissions into account, the blending ratio of biomass should be less than20%。Following the experimental investigation by thermogravimetric analysis, engineering tests are conducted in circulating fluidized beds with the capacity of25tons per hour. The boiler exhibits a stable performance when biomass ratio is less than10. Temperture in the boiler decreases with an increase of biomass ratio, resulting a relatively low combustion effieciency. Therefore, a suitable ratio and a reasonal operational condition are necessary for the circulating fluidized bed co-firing biomass and coal with high efficiency and low emissions. From the viewpoint of engineering supervision, the main considerations are suggested for modifying the circulating fluidized bed boiler system by adding biomass fuel into coal, which include important control points, information identification technology and so on.